Heart valves made from pyrolytic carbon have been used clinically for over 20 years with bileaflet, central-flow designs dominating this market; however, an increased number of clinically significant postoperative bleeding episodes have been documented for patients with mechanical valves. The long-term objective of the proposed program is to improve present-day central flow/bileaflet pyrolytic carbon valves and to accomplish these improvements with absolutely minimal changes in the material and no changes in valve design. We propose to achieve this goal by coating the pyrolytic carbon valves with CVD diamond films. The specific aims for Phase I are: 1) demonstration that CVD diamond coatings can be reliably deposited on the pyrolytic carbon surface of heart valve parts and production of sufficient numbers of coated parts for testing; 2) characterization of the deposited films for (a) uniformity of deposition, surface morphology and thickness, (b) phase purity and microstructural characterization, and (c) adhesion of the diamond film to the substrate, and 3) characterization of the chemical resistance and integrity of the coatings. Demonstration of improvements in biocompatibility and cavitation resistance is planned for Phase II.